Browsing by Organization "University of Helsinki, Helsinki Institute of Physics (HIP) (-2009)"

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  • Chatrchyan, Serguei; Anttila, Erkki; Czellar, Sandor; Härkönen, J.; Heikkinen, A.; Karimäki, V.; Kinnunen, R.; Klem, J.; Kortelainen, M.J.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, Panja; Mäenpää, T.; Nysten, J.; Tuominen, E.; Tuominiemi, J.; Ungaro, D.; Wendland, L.; CMS Collaboration (INSTITUTE OF PHYSICS PUBLISHING, 2010)
  • Chatrchyan, Serguei; Anttila, Erkki; Czellar, Sandor; Härkönen, Jaakko; Heikkinen, Mika Aatos; Karimäki, Veikko; Kinnunen, Ritva; Klem, Jukka; Kortelainen, Matti; Lampen, Pekka Tapio; Lassila-Perini, Katri Marjaana; Lehti, Sami Tapio; Linden, Tomas; Luukka, Panja; Mäenpää, Teppo H; Nysten, Jukka Sakari; Tuominen, Eija; Tuominiemi, Jorma; Ungaro, Donatella; Wendland, Lauri Andreas; CMS Collaboration (INSTITUTE OF PHYSICS PUBLISHING, 2010)
  • Chatrchyan, S.; Anttila, E.; Czellar, S.; Härkönen, J.; Heikkinen, A.; Karimäki, V.; Kinnunen, R.; Klem, J.; Kortelainen, M. J.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Nysten, J.; Tuominen, E.; Tuominiemi, J.; Ungaro, D.; Wendland, L.; CMS Collaboration (INSTITUTE OF PHYSICS PUBLISHING, 2010)
  • Mäenpää, T.; Haeggström, E.; Anttila, E.; Onnela, A.; Lampen, T.; Luukka, P.; Karimäki, V.; Tuominiemi, J. (ELSEVIER BV, 2007)
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Physical Society, 2008)
    The analysis uses data from an integrated luminosity of approximately 172 pb-1 of ppbar collisions at sqrt(s)=1.96 TeV, collected with the CDF II detector at the Fermilab Tevatron. The Lambda_b and B0 relative branching fractions are measured to be: B(Lambda_b to Lambda_c+ mu nu)/B(Lambda_b to Lambda_c+ pi) = 16.6 +- 3.0 (stat) +- 1.0 (syst) +2.6 -3.4 (PDG) +- 0.3 (EBR), B(B0 to D+ mu nu)/B(B0 to D+ pi) = 9.9 +- 1.0 (stat) +- 0.6 (syst) +- 0.4 (PDG) +- 0.5 (EBR), B(B0 to D*+ mu nu)/B(B0 to D*+ pi) = 16.5 +- 2.3 (stat) +- 0.6 (syst) +- 0.5 (PDG) +- 0.8 (EBR) This article also presents measurements of the branching fractions of four new Lambda_b semileptonic decays: Lambda_b to Lambda_c(2595)+ mu nu, Lambda_b to Lambda_c(2625)+ mu nu, Lambda_b to Sigma_c(2455)0 pi mu nu, Lambda_b to Sigma_c(2455)++ pi mu nu, relative to the branching fraction of the Lambda_b to Lambda_c mu nu decay. Finally, the transverse-momentum distribution of Lambda_b baryons produced in p-pbar collisions is measured and found to be significantly different from that of B0 mesons.
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Institute of Physics, 2008)
    A combined mass and particle identification fit is used to make the first observation of the decay B̅ s0→Ds±K∓ and measure the branching fraction of B̅ s0→Ds±K∓ relative to B̅ s0→Ds+π-. This analysis uses 1.2  fb-1 integrated luminosity of pp̅ collisions at √s=1.96  TeV collected with the CDF II detector at the Fermilab Tevatron collider. We observe a B̅ s0→Ds±K∓ signal with a statistical significance of 8.1σ and measure B(B̅ s0→Ds±K∓)/B(B̅ s0→Ds+π-)=0.097±0.018(stat)±0.009(syst).
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Institute of Physics, 2008)
    A combined mass and particle identification fit is used to make the first observation of the decay Bs --> Ds K and measure the branching fraction of Bs --> Ds K relative to Bs --> Ds pi. This analysis uses 1.2 fb^-1 integrated luminosity of pbar-p collisions at sqrt(s) = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron collider. We observe a Bs --> Ds K signal with a statistical significance of 8.1 sigma and measure Br(Bs --> Ds K)/Br(Bs --> Ds pi) = 0.097 +- 0.018(stat) +- 0.009(sys).
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth; CDF Collaboration (American Institute of Physics, 2009)
    We present the first observation in hadronic collisions of the electroweak production of vector boson pairs (VV, V=W, Z) where one boson decays to a dijet final state. The data correspond to 3.5  fb-1 of integrated luminosity of pp̅ collisions at √s=1.96  TeV collected by the CDF II detector at the Fermilab Tevatron. We observe 1516±239(stat)±144(syst) diboson candidate events and measure a cross section σ(pp̅ →VV+X) of 18.0±2.8(stat)±2.4(syst)±1.1(lumi)  pb, in agreement with the expectations of the standard model.
  • Heikkinen, Mika Aatos; Kaitaniemi, Pekka; Karimäki, Veikko; Kortelainen, Matti J; Lampen, Pekka Tapio; Lehti, Sami Tapio; Linden, Tomas; Wendland, Lauri Andreas (2010)
  • Chatrchyan, Serguei; Anttila, Erkki; Czellar, Sandor; Härkönen, Jaakko; Heikkinen, Mika Aatos; Karimäki, Veikko; Kinnunen, Ritva; Klem, Jukka; Kortelainen, Matti; Lampen, Pekka Tapio; Lassila-Perini, Katri Marjaana; Lehti, Sami Tapio; Linden, Tomas; Luukka, Panja; Mäenpää, Teppo H; Nysten, Jukka Sakari; Tuominen, Eija; Tuominiemi, Jorma; Ungaro, Donatella; Wendland, Lauri Andreas; CMS Collaboration (INSTITUTE OF PHYSICS PUBLISHING, 2010)
  • Chatrchyan, Serguei; Anttila, Erkki; Czellar, Sandor; Härkönen, Jaakko; Heikkinen, Mika Aatos; Karimäki, Veikko; Kinnunen, Ritva; Klem, Jukka; Kortelainen, Matti; Lampen, Pekka Tapio; Lassila-Perini, Katri Marjaana; Lehti, Sami Tapio; Linden, Tomas; Luukka, Panja; Mäenpää, Teppo H; Nysten, Jukka Sakari; Tuominen, Eija; Tuominiemi, Jorma; Ungaro, Donatella; Wendland, Lauri Andreas; CMS Collaboration (INSTITUTE OF PHYSICS PUBLISHING, 2010)
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Physical Society, 2009)
    We report a set of measurements of particle production in inelastic pbar{p} collisions collected with a minimum-bias trigger at the Tevatron Collider with the CDF II experiment. The inclusive charged particle transverse momentum differential cross section is measured, with improved precision, over a range about ten times wider than in previous measurements. The former modeling of the spectrum appears to be incompatible with the high particle momenta observed. The dependence of the charged particle transverse momentum on the event particle multiplicity is analyzed to study the various components of hadron interactions. This is one of the observable variables most poorly reproduced by the available Monte Carlo generators. A first measurement of the event transverse energy sum differential cross section is also reported. A comparison with a Pythia prediction at the hadron level is performed. The inclusive charged particle differential production cross section is fairly well reproduced only in the transverse momentum range available from previous measurements. At higher momentum the agreement is poor. The transverse energy sum is poorly reproduced over the whole spectrum. The dependence of the charged particle transverse momentum on the particle multiplicity needs the introduction of more sophisticated particle production mechanisms, such as multiple parton interactions, in order to be better explained.
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth; CDF collaboration (American Physical Society, 2009)
    We report a measurement of the production cross section for b hadrons in pp̅ collisions at √s=1.96  TeV. Using a data sample derived from an integrated luminosity of 83  pb-1 collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron, we analyze b hadrons, Hb, partially reconstructed in the semileptonic decay mode Hb→μ-D0X. Our measurement of the inclusive production cross section for b hadrons with transverse momentum pT>9  GeV/c and rapidity |y|<0.6 is σ=1.30  μb±0.05  μb(stat)±0.14  μb(syst)±0.07  μb(B), where the uncertainties are statistical, systematic, and from branching fractions, respectively. The differential cross sections dσ/dpT are found to be in good agreement with recent measurements of the Hb cross section and well described by fixed-order next-to-leading logarithm predictions.
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth; CDF collaboration (American Physical Society, 2009)
    We report a measurement of the production cross section for b hadrons in pp̅ collisions at √s=1.96  TeV. Using a data sample derived from an integrated luminosity of 83  pb-1 collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron, we analyze b hadrons, Hb, partially reconstructed in the semileptonic decay mode Hb→μ-D0X. Our measurement of the inclusive production cross section for b hadrons with transverse momentum pT>9  GeV/c and rapidity |y|<0.6 is σ=1.30  μb±0.05  μb(stat)±0.14  μb(syst)±0.07  μb(B), where the uncertainties are statistical, systematic, and from branching fractions, respectively. The differential cross sections dσ/dpT are found to be in good agreement with recent measurements of the Hb cross section and well described by fixed-order next-to-leading logarithm predictions.
  • Aaltonen, T.; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Institute of Physics, 2009)
    We present a measurement of the transverse momentum with respect to the jet axis (kt) of particles in jets produced in pp̅ collisions at √s=1.96  TeV. Results are obtained for charged particles in a cone of 0.5 radians around the jet axis in events with dijet invariant masses between 66 and 737  GeV/c2. The experimental data are compared to theoretical predictions obtained for fragmentation partons within the framework of resummed perturbative QCD using the modified leading log and next-to-modified leading log approximations. The comparison shows that trends in data are successfully described by the theoretical predictions, indicating that the perturbative QCD stage of jet fragmentation is dominant in shaping basic jet characteristics.
  • Aaltonen, T.; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Institute of Physics, 2008)
    We report a measurement of the single top quark production cross section in 2.2 ~fb-1 of p-pbar collision data collected by the Collider Detector at Fermilab at sqrt{s}=1.96 TeV. Candidate events are classified as signal-like by three parallel analyses which use likelihood, matrix element, and neural network discriminants. These results are combined in order to improve the sensitivity. We observe a signal consistent with the standard model prediction, but inconsistent with the background-only model by 3.7 standard deviations with a median expected sensitivity of 4.9 standard deviations. We measure a cross section of 2.2 +0.7 -0.6(stat+sys) pb, extract the CKM matrix element value |V_{tb}|=0.88 +0.13 -0.12 (stat+sys) +- 0.07(theory), and set the limit |V_{tb}|>0.66 at the 95% C.L.
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Physical Society, 2009)
    We present measurements of the top quark mass using the \mT2, a variable related to the transverse mass in events with two missing particles. We use the template method applied to t\tbar dilepton events produced in p\pbar collisions at Fermilab's Tevatron and collected by the CDF detector. From a data sample corresponding to an integrated luminosity of 3.4 \invfb, we select 236 t\tbar candidate events. Using the \mT2 distribution, we measure the top quark mass to be M_{Top} = 168.0^{+4.8}_{-4.0} $\pm$ {2.9} GeV/c^{2}. By combining the \mT2 with the reconstructed top mass distributions based on a neutrino weighting method, we measure M_{top}=169.3 $\pm$ 2.7 $\pm$ 3.2 GeV/c^{2}. This is the first application of the \mT2 variable in a mass measurement at a hadron collider.
  • Aaltonen, T.; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth (American Institute of Physics, 2008)
    We report a measurement of the top quark mass $M_t$ in the dilepton decay channel $t\bar{t}\to b\ell'^{+}\nu'_\ell\bar{b}\ell^{-}\bar{\nu}_{\ell}$. Events are selected with a neural network which has been directly optimized for statistical precision in top quark mass using neuroevolution, a technique modeled on biological evolution. The top quark mass is extracted from per-event probability densities that are formed by the convolution of leading order matrix elements and detector resolution functions. The joint probability is the product of the probability densities from 344 candidate events in 2.0 fb$^{-1}$ of $p\bar{p}$ collisions collected with the CDF II detector, yielding a measurement of $M_t= 171.2\pm 2.7(\textrm{stat.})\pm 2.9(\textrm{syst.})\mathrm{GeV}/c^2$.
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth; CDF collaboration (American Physical Society, 2009)
    We present a measurement of the tt̅ production cross section in pp̅ collisions at √s=1.96  TeV using events containing a high transverse momentum electron or muon, three or more jets, and missing transverse energy. Events consistent with tt̅ decay are found by identifying jets containing candidate heavy-flavor semileptonic decays to muons. The measurement uses a CDF run II data sample corresponding to 2  fb-1 of integrated luminosity. Based on 248 candidate events with three or more jets and an expected background of 79.5±5.3 events, we measure a production cross section of 9.1±1.6  pb.
  • Aaltonen, Timo; Mehtälä, Petteri; Orava, Risto; Mäki, Tuula; Saarikko, Heimo; Österberg, Kenneth; CDF collaboration (American Physical Society, 2009)
    We present a measurement of the tt̅ production cross section in pp̅ collisions at √s=1.96  TeV using events containing a high transverse momentum electron or muon, three or more jets, and missing transverse energy. Events consistent with tt̅ decay are found by identifying jets containing candidate heavy-flavor semileptonic decays to muons. The measurement uses a CDF run II data sample corresponding to 2  fb-1 of integrated luminosity. Based on 248 candidate events with three or more jets and an expected background of 79.5±5.3 events, we measure a production cross section of 9.1±1.6  pb.